Article: With less Arctic ice, more storms like Sandy

Mar. 11, 2013

The wreckage of a house in the Holgate section of Long Beach Township in the aftermath of Sandy, the storm some are calling the most destructive ever to hit the New Jersey coast. Scientists are saying climate changes is driving a loss of Arctic sea ice that in turn is affecting weather patterns across North America. / Robert Ward/Staff Photographer

Written by

Kirk Moore | @KirkMooreAPP

A warming global climate that melts sea ice in the Arctic is driving changes to the jet stream — upper atmospheric winds that shape weather across North America — and helped create the conditions that mutated Hurricane Sandy into a hybrid storm, say scientists who eerily predicted that scenario weeks before the storm hit Oct. 29.

Expect more of the same, authors Charles H. Greene, Jennifer Francis and Bruce C. Monger say in a new article published in the scientific journal Oceanography.

“Since the ice has been disappearing, we’ve seen the jet stream take a more wavy pattern,” said Francis, a research professor with the Institute of Marine and Coastal Sciences at Rutgers University, studying the Arctic region and its role in climate change.

“It increases the chances of cold Arctic air breaking out to the middle latitudes,” said Greene, director of the Ocean Resources and Ecosystems Program at Cornell University, who studies how the loss of sea ice is leading to slow heating of upper ocean levels in the Arctic.

“Unlike a typical hurricane, this huge and powerful hybrid storm did not lose energy after making landfall because it was supercharged with energy derived from a southward dip in the jet stream over the Mississippi Valley that ushered in an invasion of cold Arctic air,” the researchers write in their article.

Temperature differences between the Arctic and areas to the south historically have driven the jet stream in a fast band around the Earth’s northern hemisphere, with occasional dips and detours. But with the temperature differential changing, the jet stream is starting to look like an old river, with more frequent bends and turns, Greene and Francis said.

Warming also reduces a wind pattern called the polar vortex, circular movement that otherwise tends to keep cold air swirling around the north end of the globe, Greene said.

(Page 2 of 2)

The scientists were part of a research team working with the National Oceanic and Atmospheric Administration, a project that published an attention-grabbing report last year. Their studies showed that jet stream shifts would lead to more frequent downdrafts of frigid polar air, increasing the strength of winter storms, a possibly disrupting the historic common path taken by tropical storm systems as they approach the continent.

Within weeks, those predictions seemed to be borne out. As Sandy steamed into the Caribbean, forecasters and their computer models could see the jet stream lowering and dropping a massive area of cold air just in time for Sandy’s arrival on the East Coast. Hurricanes draw their energy from warm ocean water, but the arrival of cold air from the north assured Sandy would become an extratropical cyclone — like last week’s winter storm, drawing its energy from temperature differences between air masses, Greene said.

“It was chilling to watch this scenario unfold,” said Francis, an experienced sailor who made her way around the world and now lives on the South Shore of Massachusetts.

The new report proposes that jet stream shifts produced the other critical factor in Sandy: the area of high pressure over Greenland and northeast Canada that made the storm hang a sharp left-hand turn straight into the New Jersey coast, its center making landfall around Brigantine.

Uncharted territory

“That blocking pattern is what made Sandy make that strong left turn, which has never been observed before,” Greene said. The storm’s shift to extratropical force just before landfall was never seen in modern times either. Low air pressure, the measure of a powerful storm, in Sandy included “some of the lowest pressures that have been measured that far north,” Greene said.

The high pressure block created “a huge area of violent east winds that pushed water up against the eastern seaboard from Nova Scotia to New Jersey, greatly exacerbating the storm surge,” the authors wrote. “To literally top it off, the storm surge combined with full-moon tides and huge ocean waves to produce record-high water levels that exceeded the worst-case predictions for certain parts of New York City.”

“Now, some may argue that this was just a series of unfortunate events resulting from the coincidence of many rare and/or unprecedented acts of nature,” the authors acknowledged. But they argue “the loss of summertime Arctic sea ice due to greenhouse warming stacks the deck” to favor bigger meanders in the jet stream, more breakouts of Arctic air into the United States and more frequent atmospheric blocks that can deflect hurricanes onto shore.

On the Monday Sandy hit, Greene recalled, he gave a lecture to his big class for basic oceanography. The topic was climate change. As part of the lecture, he showed a map of what New York City would look like with the 3-foot rise in the sea level that many scientists predict by 2100.

“And, by the way,” he told the students, “this is what it’s going to look like in New York City tonight.”